The present invention is directed generally to a vacuum deposition apparatus and method, and specifically to an apparatus and method which includes an air to vacuum seal and an accumulator.
Interest in thin-film photovoltaics has expanded in recent years. This is due primarily to improvements in conversion efficiency of cells made at the laboratory scale, and the anticipation that manufacturing costs can be significantly reduced compared to the older and more expensive crystalline and polycrystalline silicon technology. The term “thin-film” is used to distinguish this type of solar cell from the more common silicon based cell, which uses a relatively thick silicon wafer.
Thin-film solar cells may be manufactured using a roll-to-roll coating system based on sputtering, evaporation or chemical vapor deposition (CVD) techniques. A thin foil substrate, such as a foil web substrate, is fed from a roll in a linear belt-like fashion through the series of individual vacuum chambers or a single divided vacuum chamber where it receives the required layers to form the thin-film solar cells.
Since the deposition process takes place in a vacuum, the foil roll may have to be either be placed inside a vacuum chamber itself, thus complicating the process and apparatus, or providing the foil web into a sealed passage, stopping the foil web, pumping down the passage, and then restarting the foil web by passing it from the pumped down passage into and out of the vacuum chamber(s) in which the various layers are deposited onto the foil.
In such a system, the foil is supplied on a roll and has a finite length. To provide a continuously fed foil layer, the end of a new roll must be coupled to the end of the previous roll. This involves stopping the original web foil, attaching the new web foil leading end to the tail end of the original web foil and then feeding the new web foil into the coating apparatus.